1. Field of the Invention
The present invention relates to a piezo-resonator utilizing thickness shear vibration, and more particularly, it relates to an improvement for attaining improved electric characteristics in such a piezo-resonator.
2. Description of the Background Art
FIG. 11 shows a conventional elongated rectangular piezo-resonator 101 forming a ceramic discriminator utilizing thickness shear vibration, which is of interest to the present invention.
The piezo-resonator 101 comprises an elongated rectangular piezoelectric substrate 102. Referring to FIG. 11, solid lines show elements which are formed on a first major surface of the piezoelectric substrate 102, while broken lines show those formed on a second major surface, respectively.
On the first major surface of the piezoelectric substrate 102, first and second excitation electrodes 103 and 104 are arranged along the longitudinal direction of the piezoelectric substrate 102. The second excitation electrode 104 is closer to a first longitudinal end portion 105 of the piezoelectric substrate 102 than the first excitation electrode 103, while both of the first and second excitation electrodes 103 and 104 are closer to the first end portion 105 than a longitudinal central portion of the piezoelectric substrate 102.
Furthermore, on the first major surface of the piezoelectric substrate 102, a first terminal electrode 107 is formed on a second longitudinal end portion 108 of the piezoelectric substrate 102, and connected to the first excitation electrode 103 through a first lead line 106, which passes through the longitudinal central portion of the piezoelectric substrate 102. A second terminal electrode 110 is formed on the first longitudinal end portion 105 of the piezoelectric substrate 102, and connected to the second excitation electrode 104 through a second lead line 109.
On the second major surface of the piezoelectric substrate 102, an earth electrode 111 is formed so as to be simultaneously opposed to both of the first and second excitation electrodes 103 and 104. An earth terminal electrode 113 is formed on the longitudinal central portion of the piezoelectric substrate 102 and connected to the earth electrode 111 through an earth lead line 112, as shown by the broken lines in FIG. 11.
In the piezo-resonator 101 having the aforementioned structure, the opposed portions of the first and second excitation electrodes 103 and 104 and the earth electrode 111 are adapted so as to vibrate.
In the aforementioned piezo-resonator 101, however, not only the excitation electrodes 103 and 104 and the earth electrode 111, but also the first lead line 106 and the earth terminal electrode 113 are opposed to each other through the piezoelectric substrate 102.
Such a piezo-resonator 101 is generally obtained by forming conductor films which define the excitation electrodes 103 and 104, the earth electrode 111, the lead lines 106, 109 and 112 and the terminal electrodes 107, 110 and 113, on a polarized mother piezoelectric substrate and thereafter cutting the mother piezoelectric substrate. The long edges of the piezoelectric substrate 102, shown in FIG. 11, are provided as a result of such cutting. According to this manufacturing method, the conductor film which defines the earth terminal electrode 113 is generally formed to extend in the form of a strip on the mother piezoelectric substrate, in a similar manner to the remaining conductor films which define the excitation electrodes 103 and 104, the earth electrode 111 and the first and second terminal electrodes 107 and 108. In the piezo-resonator 101 obtained by such cutting, therefore, the earth terminal electrode 113 is partially opposed to the first lead line 106.
Such an overlap of the earth terminal electrode 113 and the first lead line 106 results in vibration in this portion. Such undesired vibration causes a ripple effect in a demodulation distortion factor characteristic, so as to reduce the demodulation distortion factor characteristic.
Under the present circumstances, the aforementioned undesired vibration is damped by solder which is employed for mounting a lead terminal on the earth terminal electrode 113. However, due to dispersion in the amount of solder and in the soldering area, it is difficult to reliably damp such undesired vibration.